This invention relates to interferometry, and more particularly to an interferometry apparatus and method utilizing a phase-conjugate mirror.
Optical interferometers are known which make use of the interference phenomenon known as the "speckle effect"--the speckled pattern of laser light when reflected from a rough surface. One prior-art speckle interferometer takes the form of a Michelson-type instrument in which the mirror of one arm is replaced by a scattering surface. Provided that the coherence of the laser light is sufficiently high, speckles are formed by interference between light from the reference-beam arm and the light scattered retro-reflectively from the rough surface. Translating the scattering surface in the direction of the incident light causes each speckle to vary in brightness cyclically, from light to dark, independently from its neighbor, in a similar way that points on the equivalent Michelson mirror would appear to fluctuate in brightness as interference fringes sweep across it when the mirror is moved. The visual speckle interferometer can thus be used for detecting movement, but not for measuring the displacement that has taken place. Further, since a plane wave with uniform amplitude serves as the reference for the speckle wave, the plane wave cannot be matched to the random variation of amplitude over the speckle pattern. Thus, the visibility (or contrast) of the interference pattern cannot be made the same throughout the field.